Among the factors limiting the open circuit voltage of Heterojunctions with Intrinsic Thin layers solar cell, the surface potential barrier at the Indium Tin Oxide (ITO)/hydrogenated amorphous silicon (a-Si:H) interface is one of the most important. To reduce this surface potential barrier, we have varied the band bending by simulation. The aim is to understand why, in spite of a considerable change in the front contact barrier height at the interface ITO/n-a-Si:H (band banding reduced), the characteristics J(V) remain almost unchanged.